1. Field of the Invention
This invention relates to a process for hydrodewaxing a hydrocarbon oil feedstock. More particularly, this invention is concerned with a catalytic process for hydrodewaxing a hydrocarbon oil feedstock such as a light hydrocarbon feedstock. It is further concerned with a process for manufacturing a high Viscosity Index (VI) distillate lubricating oil stock of low pour point and with good yield.
In the hydrodewaxing process of this invention a light waxy hydrocarbon oil feedstock, for example, and hydrogen are contacted at an elevated temperature and pressure with a catalyst composition comprising a specified amount of an oxide of a Group VIII metal, such as an oxide of nickel or cobalt and an oxide of a Group VIB metal, such as an oxide of molybdenum or tungsten, supported on a porous support comprising a matrix or binder and a ZSM-5 type crystalline aluminosilicate zeolite and wherein the said support has a polyoxymetalate-modified surface.
In the catalytic hydrodewaxing process of this invention a hydrocarbon oil feed, such as a waxy hydrocarbon fraction, is contacted with hydrogen and the surface-modified catalyst in a manner such that a high viscosity index developed hydrocarbon oil is achieved in high yield.
2. Prior Art
Paraffin distillates and residual oils leaving the refinery crude stills contain wax and are normally solids at ambient temperatures. The deasphalting and refining processes increase the wax content of the lube feedstocks. Removal of the wax from these fractions is necessary to permit the manufacturing of lubricating oils with the desired low temperature properties. Catalytic and solvent dewaxing are the major processes used in the petroleum industry today for removing this wax.
The catalytic dewaxing process works by selectively cracking the waxy molecules over a zeolite catalyst. This differs from solvent dewaxing, where the wax is removed from the oil based on its solubility when dissolved in a suitable solvent. These different mechanisms for wax removal give the dewaxed oil product from the two processes different properties. Generally, the dewaxed oil from solvent dewaxing is obtained in a higher yield and has a higher viscosity index (VI) than that obtained from catalytic dewaxing. The loss in yield and VI observed for catalytic dewaxing compared with solvent dewaxing the same feedstock is called the yield and VI penalty. It is desirable to produce dewaxed oil from catalytic dewaxing without any yield or VI penalty.
The presently available commercial catalytic dewaxing processes which utilize a ZSM-5 containing catalyst work well for producing the heavy neutral oils and bright stocks. However, these processes suffer from severe yield and VI penalties when processing lighter feedstocks. A catalyst capable of dewaxing a light feedstock to a low pour, high VI product without dewaxed oil yield loss is not currently available.
A number of other processes for catalytic dewaxing of hydrocarbon oils to reduce the temperature at which separation of waxy hydrocarbons occurs have been described in the art.
U.S. Pat. No. 4,743,355 discloses a process in which a waxy hydrocarbon feedstock is converted into a high quality lube oil stock of reduced pour point by hydrodewaxing the feedstock in the presence of catalyst comprising, for example, a porous refractory oxide such as alumina and a crystalline zeolite having a ZSM-5 zeolite structure and passing a portion of the effluent from the hydrodewaxing zone to a hydrocracking zone where it is a hydrocracking catalyst under conditions such that a further reduction in pour point is effected.
U.S. Pat. No. 4,458,024 teaches a single stage hydrotreating and hydrodewaxing process in which a petroleum residua is contacted with a catalyst comprising a ZSM-5 zeolite in an alumina binder. The catalyst employed has about 80% of its pore volume in pores no greater than 100 Angstroms in diameter and at least 90% of its pore volume in pores no greater than 150 Angstroms in diameter.
U.S. Pat. No. 3,668,113 discloses a process in which a hydrocarbon fraction is reduced in sulfur and n-paraffin wax content by first contacting the hydrocarbon fraction with a catalyst comprising a hydrogenating component and a crystalline mordenite to remove n-paraffin wax and then contacting the dewaxed fraction with a catalyst comprising a hydrogenating component on a refractory inorganic oxide to remove sulfur.
U.S. Pat. No. 3,700,585 teaches a dewaxing process in which a petroleum feedstock having a boiling point above 350.degree. F. is contacted with a zeolite ZSM-5 or ZSM-8 having an associated hydrogenation component and, optionally, in the presence of hydrogen.
U.S. Pat. No. 3,894,938 discloses a process for dewaxing and desulfurizing high pour point high sulfur gas oil in which the gas oil is first contacted with a ZSM-5 type zeolite which may contain a hydrogenation component in the presence or absence of added hydrogen followed by conventional hydrodesulfurization processing.
U.S. Pat. No. 3,980,550 discloses a process for dewaxing a gas oil by contacting the gas oil with hydrogen in the presence of a catalyst such as a ZSM-5 type having at least one multi valent transition metal.
U.S. Pat. No. 4,229,282 teaches a catalytic dewaxing process in which a hydrocarbon oil is contacted in the presence of hydrogen with catalyst comprising a dense zeolite, such as a dense ZSM-5 zeolite and a hydrogenation component.
U.S. Pat. No. 4,810,357 discloses a process for dewaxing relatively heavy or relatively light lube chargestocks in two parallel separate reactors where the catalyst employed in the reactor used for dewaxing the relatively light chargestock is a zeolite catalyst such as ZSM-22, ZSM-23 or ZSM-35 while in the reactor used for dewaxing the relatively heavy chargestock the catalyst used is a zeolite such as ZSM-5, ZSM-11, etc.
U.S. Pat. No. 4,510,044 discloses a single stage hydrodewaxing and hydrotreating process in which hydrogen and a petroleum residua is contacted with a catalyst comprising a ZSM-5 type zeolite in an alumina binder having a hydrogenation component and having 90% of its pore volume in pores no greater than 150 Angstroms in diameter.
U.S. Pat. No. 4,203,869 teaches a process for preparing a crystalline aluminosilicate zeolite having an aluminum-free outer shell of crystalline SiO.sub.2 where the zeolite is prepared by (1) initiating crystallization in a crystallization medium to produce the zeolite and then altering the crystallization medium to eliminate the aluminum therein where the outer shell of SiO.sub.2 has the same crystal structure as the zeolite.
U.S. Pat. No. 3,725,302 discloses a process in which the external surfaces of crystalline aluminosilicates are treated with hydrocarbyl halosilanes or their condensation products with ammonia, primary amines, secondary amines or alcohols to modify the surface adsorptive properties of the aluminosilicates. Useful hydrocarbyl halosilanes include trimethylchlorosilane, triphenylchlorosilane, etc.
U.S. Pat. No. 4,447,583 teaches a method for preparing a composition comprising a crystalline zeolite such as ZSM-5 coated with silica that extensively covers and resides on the external surfaces thereof. Silicon-containing compounds employed in the coating process include diethylsilicone, phenylethylsilicone, methyltrifluoropropylsilicone, methylvinylsilicone, etc.
U.S. Pat. No. 4,950,835 teaches a process for preparing a catalyst through vapor phase disposition of Si on the surface of an HZSM-5 catalyst obtained by ion exchanging ZSM-5 catalyst. Useful silicon sources include tetraalkyl orthosilicate or tetraalkoxysilane.
U.S. Pat. No. 4,138,363 discloses hydrophilic silane-zeolite compositions formed by condensing a hydrophilic silane, such as methyltrichlorosilane, gamma-amino-propyltrimethoxylsilane, etc., onto the surface of a hydrated zeolite.
European Patent Application 88120998.5 of Dec. 15, 1988 teaches a process for preparing p-ethylphenol utilizing a catalyst of a crystalline aluminosilicate, such as a ZSM-5 zeolite, incorporating a specific amount of an alkoxysilane.